Today sees the official launch at the House of Commons of Medical Justice (MJ), a network of health professionals, lawyers and former detainees who go into immigration detention centres pro bono to help distressed detainees. "All of those who work with detainees share experience of neglect, discrimination and abuse on a scale that is saddening and frightening," says Alexander Goodman, MJ's chair and a barrister.

This neglect and abuse flourished under Tony Blair's watch. Perhaps Gordon Brown will exercise a little more humanity now he's in control. He should take note of what Medical Justice is saying.

In the past two years MJ has assisted more than 500 detainees. It has had successes - 200 of those it has seen have been released, there have been improvements in policy and treatment. The chief inspector of prisons held a healthcare inquiry at MJ's instigation at Yarl's Wood in Bedfordshire after a Ugandan woman was reduced to mental collapse. Detainees are now less often routinely handcuffed while escorted to hospital. But the abuse and neglect continue, so much so that Alexander Goodman says the only hope is to close the centres down altogether.

Some 2,220 men women and children are held in the UK's 10 immigration detention centres. Though given no release date - they can be held indefinitely unlike prisoners held for crimes - they can be suddenly and forcibly removed with very little notice. There are those who would say nobody asked these detainees to come here, what do they expect? After a piece like this is published, people send emails presenting seemingly articulate and reasonable arguments for detention and deportation. But however reasonable they make it sound, only a dehumanised brute would condone the neglect meted out to these people and their children.

To coincide with its launch today, MJ has published a concise and horrifying report entitled Beyond Comprehension and Decency, An Introduction to the Work of Medical Justice. MJ got going after Harris Nyatsanza and about 100 others went on hunger strike at several detention centres in June 2005. The centre management refused to send Nyatsanza to hospital. He was on the verge of suffering organ failure when Frank Arnold, doctor and MJ founder, got him transferred to hospital.

A couple of weeks ago Nyatsanza, a Zimbabwean MDC activist, was finally given refugee status. He told me that he went on hunger strike and attempted suicide not only because of despair and the terror of what a return to Zimbabwe would mean, but because it was the one thing the authorities in the detention centre couldn't control. When he recovered, Nyatsanza, Arnold and others formed MJ. There were 16 at the first meeting, the membership now numbers over 300.

Working for free, occasionally through legal aid, MJ volunteers produce medical reports and fight legal battles for those for whom legal aid is restricted to five hours per case, (it may be further reduced in the autumn). If it weren't for them, many more human rights abuses would be going on out of sight. MJ is not alone in its criticisms of asylum detention.

The chief inspector of prisons has been heavily critical, saying: "People are languishing in unsafe detention centres because of the inefficiencies and chaos of the Home Office." Amnesty International has voiced similar condemnations.

Home Office rules stipulate that torture victims should only be locked up in exceptional circumstances for short periods. But MJ has found many cases where evidence of rape and torture has gone undocumented and uninvestigated by detention centre medical staff. Of 56 cases studied, MJ found 20 allegations of torture had been ignored. It has cases of people held for years. MJ frequently finds medical needs have not been diagnosed and that those subcontracted to deliver healthcare by the private profit-making companies running seven of the 10 centres lack expertise. In the three centres run by the prison service, detainees are seen by NHS professionals who are far more accountable. It would be safer for all detainees to be treated by NHS staff.

MJ documents cases of undiagnosed infectious TB and people with HIV/Aids going without medication. Thanks to pressure from these doctors and lawyers, the Home Office has revised its former practise of returning children to sub-Saharan African countries without vaccination or prophylaxis against malaria. It was too late for six patients MJ knows of who developed malaria following their return. Of 11 patients seen during or after hunger strikes in the centres, six were in imminent danger of organ failure. There was no Home Office policy or guidance for detention centre staff dealing with the dangers of reintroducing food after a hunger strike. Half of the group studied were diagnosed with symptoms of post-traumatic stress disorder; many had self-harmed or attempted suicide.

They quote horrifying cases: a gay man from a Muslim country with cigarette burns recorded as shrapnel wounds, a mistake almost impossible to make for anyone properly trained. A 30-year-old Ugandan tour-guide sought asylum after a group of tourists were butchered in front of him; the soldiers subsequently arrested, beat and tortured him. He fled to the UK where he was immediately detained. Three months later he was issued with a removal date, attempted suicide and was bailed. He then had a daughter with an Englishwoman with whom he was in a long-term relationship. On Christmas Eve last year he was detained again and took an overdose. He has been released after MJ intervention. Attempts were made to remove a young west African woman who had been repeatedly raped and tortured by soldiers. An immigration officer threatened that unless she complied with deportation, the army in her home country would be told she was coming back. A Ghanaian diabetic with hypertension told medical staff in Yarl's Wood she was pregnant, despite a test which proved negative. They didn't repeat it to make certain. She miscarried and produced the foetus in a bucket.

MJ's report lives up to its title. Dig a little beneath the ignorance and what you find is, as they say, beyond comprehension and decency.